The problems presented by substances which deplete the atmospheric ozone layer were dealt with at Montreal, where the protocol was signed imposing a reduction in the production and use of chlorofluorocarbons (CFCs). This protocol has been the subject of amendments which have required the abandoning of CFCs and have extended regulation to other products, including hydrochlorofluorocarbons (HCFCs).
The refrigeration and air conditioning industry has invested a great deal in the replacement of these refrigerants and it is because of this that hydrofluorocarbons (HFCs) have been marketed.
In the motor vehicle industry, the air conditioning systems of commercial vehicles have been changed in many countries from a chlorofluorocarbon (CFC-12) refrigerant to a hydrofluorocarbon (1,1,1,2-tetrafluoroethane: HFC-134a) refrigerant, which is less harmful to the ozone layer. However, from the viewpoint of the objectives set by the Kyoto protocol, HFC-134a (GWP=1430) is regarded as having a high heating power. The contribution of a refrigerant to the greenhouse effect is quantified by a criterion, the GWP (Global Warming Potential), which summarizes the heating power by taking a reference value of 1 for carbon dioxide.
Hydrofluoroolefins (HFOs) have a low heating power and thus meet the objectives set by the Kyoto protocol. Document JP 4-110388 discloses 2,3,3,3-tetrafluoropropene (HFO-1234yf) as a heat transfer agent in refrigeration, air conditioning and heat pumps.
In the industrial sector, the refrigerating machines most commonly used are based on cooling by evaporation of a liquid refrigerant. After vaporization, the refrigerant is compressed and then cooled in order to return to the liquid state and thus continue the cycle.
For economic reasons, refrigerant compressors are very often reciprocating compressors with lubricated cylinders. In general, internal lubrication of the compressors is essential in order to reduce wear and heating of the moving members, complete their leaktightness and protect them against corrosion.
The principal characteristics required of oils intended for refrigerant compressor lubrication are miscibility with the refrigerant, solubility, and thermal and chemical stability.
Thus, polyalkylene glycols (PAGs) have been developed as lubricants of HFC-134a in motor vehicle air conditioning.
Document U.S. Pat. No. 7,534,366 recommends the use of a PAG, in the form of a homopolymer or copolymer consisting of 2or more oxypropylene groups and having a viscosity of 10 to 200 centiStokes at 37° C., in combination with HFO-1234yf in air conditioning.